report line number counter

I have a report for a list like this
Tipogra: 2012 Provvisoria

Category: Specialisti e Odontoiatri

Sub Category: ALLERGOLOGIA

Name Points

CRISTIANO 11,98

MASSIMO 10,19
Sub Category: BIOCHIMICA CLINICA

Name Points

ERMELINDA 7,00
Sub Category: CARDIOLOGIA

Name Points

DONATELLA 17,58

SALVATORE 11,68

CLAUDIA 11,31

CINZIA 9,04
i need to have the line number for each sub category like this:
Tipogra: 2012 Provvisoria

Category: Specialisti e Odontoiatri

Sub Category: ALLERGOLOGIA

Position Name Points

1 CRISTIANO 11,98

2 MASSIMO 10,19
Sub Category: BIOCHIMICA CLINICA

Position Name Points

1 ERMELINDA 7,00
Sub Category: CARDIOLOGIA

Position Name Points

1 DONATELLA 17,58

2 SALVATORE 11,68

3 CLAUDIA 11,31

4 CINZIA 9,04

can help me?

thanks